Document LinearFold+mfe and make linters work

I merged much of linearfold directly from https://github.com/allyourbasepair/rbscalculator - and so, not only are the linters *very* unhappy, but there are lots of missing spots for better documentation (though vivek did very well in most of the code).

I am putting a documentation issue here: squash all linter bugs, add documentation and context for everything in the LinearFold+mfe packages, and generally clean it up to be up-to-spec with the rest of the project.

I am adding it now because I believe we need to get it into the tree, then can begin improvements in an iterative process.

Locate the LinearFold and mfe packages, then run the project's linters to identify the reported problems. Done means the linter issues are resolved and the packages have documentation and context consistent with the rest of the project.

Written by the indexing model from the issue text.